The present invention relates to an apparatus for the pneumatic conveyance of pulverized or granulated material between collection units and drawing stations with the extraction of the same material from the flow line during conveyance.
The apparata to which the present invention relates are employed to transfer loose pulverized or granulated material (e.g. flour, corn, granulated plastic material and the like) from collecting silos towards drawing stations wherein the flow of material is interrupted. In these, the material is weighed and discharged onto the machines which employ it. To perform said transfer, a pneumatic line is employed, wherein the air, in aspiration or in compression, conveys the material from the collecting silos towards the drawing stations. These are composed, in conventional apparata, of a decanting cyclone inside which the air is separated from the powders. In particular, the latter fall downwards towards the output of the cyclone which is controlled by a system of valves which are operated by a reducer, while the air originating from the pneumatic line is discharged upwards and conveyed inside filters to separate the residues of power which is still carries. The filtered air is then finally discharged into the environment where the drawing stations are accommodated.
The conventional apparata described above have many disadvantages. Among these, the need to employ a cyclone fitted with valves with a related reducer and a filter, provided in each material drawing point from the pneumatic line; the use of a system of routing valves to route the powders towards the various drawing stations, the number of which cannot obviously increased beyond that of the routings allowed by the valve; the significant bulk represented by the expensive cluster of cyclones and associated filters, the installation of which requires very spacious and high accommodations.
Still another disadvantage lies in the discharge into the environment occupied by the drawing stations of a certain amount of pulverized material dragged along by the air leaving the filters.
The most serious problem, however, is represented by the elimination of the "trailings" or residues of material which remain in the pneumatic line of known apparata. Actually, once the required weighing or metering values of the material are achieved, the valves which control the discharge thereof are closed and significant amounts of material are trapped in the cyclones. This, if discharged, alters the desired values, having a negative effect on the preset mixtures, and the consequences on the costs of recovering the residues are similarly negative. For the recovery and the elimination of the trailings, conventional apparata may comprise a plurality of separate silos for collecting the residues, which makes the apparatus even more complicated, expensive and bulky. The operations related to these recoveries furthermore extend the overall material processing times. The residues, on their part, complicate and hinder the adjustment of the devices of the apparatus, which must be conventionally controlled by electronic controls which easily give rise to problems. These problems are all the more relevant, if it is considered that the circulating material can be of a different nature, and therefore require a specific and selective control of its conveyance.